Around '05, or '06, GM combined the OnStar antenna and the XM antenna. However, this may not mean that XM is included. I tried to find the RPO code for XM installed, but there are so many I gave up. Most GM radios use a separate receiver for XM, it is a small module mounted behind the dash and plugged into the radio. I wish I had the RPO code, we could tell if you have the module.